The zebrafish is a vertebrate animal that can regenerate several adult tissue types. These include well-studied structures such as fins, heart and eyes, but also poorly studied ones, such as the whisker-like facial barbels. The zebrafish maxillary barbel (ZMB) contains skin cells, glands, taste buds, connective tissues, nerves, and vascular components. Because the transparent barbells are external, all of the differentiated cell types within are visible and experimentally accessible. Barbels are known to regenerate in other species of fishes, but have not been studied for this capacity in zebrafish. Based on studies to date, we hypothesize that Wnt signaling molecules and glypican co- receptors are critical for both ZMB outgrowth and regeneration after injury. In our first aim, we will document patterns of cell division and cell death during development and regeneration of this appendage, and confirm the existence and function of the barbel lymphatics, which we are the first to describe. In the second aim, we will 1) map the spatial and temporal resolution of non-canonical Wnt ligands and receptors (glypicans and frizzleds) in ZMB tissue, 2) use transgenic fish to test if restoring glypican function restores ZMB outgrowth in a zebrafish mutant, 3) survey if canonical Wnt signaling is required for ZMB budding and regeneration, and 4) test candidate genes in the ZMB using a morpholino approach. Knowledge gained from these investigations will contribute significantly to our understanding of the genetic interactions involved in the development and maintenance of skin and skin appendages. Because the ZMB is an adult organ that regenerates, this study will also illuminate the response to injury of many terminally differentiated cell types, including blood vessels, lymphatics and nerves. Unlike regeneration in the zebrafish caudal fin, regeneration in the ZMB is characterized by abnormal cell proliferation and extracellular matrix deposition, a process that may be relevant to vertebrate wound healing pathologies such as keloids and/or hypertrophic scars. The ability of zebrafish barbel nerves to regrow axons to their taste bud targets may suggest approaches to restore peripheral sensation to traumatized tissues. Finally, the availability within the ZMB of both a capillary loop and a large, accessible lymphatic is an attractive system in which to study the physiological and pathological functions of the vasculature, including fluid balance and tumor metastasis. )